The writer Huysmans described Forain as a supreme painter of prostitutes and low-life. Forain even illustrated Huysmans book Martha which was the first novel in French about the life of a licensed prostitute. Some people have described your work as pornographic, but other people only see it depicting the kind of consensual encounters that many of us have experienced or at least fantasised about? Why do you think people are so enraged?

Well, I actually don't think they really are. I think that when my critics have accused me of producing work that’s pornographic, or in the case of Duncan Macmillan of saying that my work is "instantly forgettable", and that I'm "welcome to paint as long as no one takes him seriously" I think that it's very uncharitable - the way that a thug would use a baseball bat, just to try and knock you out. It's as if they're going for broke, saying "Look, this isn't an artist, he's a pornographer and he's a bad one at that!" So that's me dealt with!

It's irresponsible, and I just don't see that at all, I just don't see it. But what I do see is that a lot of my darker work is popular because it depicts a world that, like it or not, we all know about and, despite ourselves, often find fascinating. I've spoken to many people over the years and believe that inside everybody lurks a fallen angel. Most people have got a fetish or dark secret about something or other, but will not talk about it, and rightly so. Of course I don't think you should be sat on a bus saying, "Yeah, you know, I like high heels, I love them!" to some stranger, but I think women are particularly adept at having these desires. The women I've known are very sensuous creatures - much better equipped for the sexual world than we are.

I can't help but wonder whether an artist's work is taken more seriously if you're seen to be painting drug problems or social deprivation or industrial decline? Perhaps people think of this as being meaningful, but consider painting sex to be cheap and nasty? Yet we're wired to reproduce and it's hardly surprising that I want to make this my subject matter. The people in my paintings are people like me - driven into sexual world, and they know they're going to be disappointed and they know that they're going to mess up their minds, mess up somebody else's mind, but the desire is so strong - whether it's a sexual thing or an egotistical thing, I can't quite work out.

But doesn't this just bring continual disappointment?

My experience is that it is, yeah, because I don't think that a healthy relationship is a purely sexual one - it just can't be. The people I paint know it's not going to end happily, it's not a fairytale, that they'll loose people that care for them, they'll make a complete arse of themselves in public, because to want somebody is such a powerful emotion. You've got to be very disciplined to walk away from it and most people can't.

You speak from experience?

Before my work was recognised I was always scared because I had a wife, or I was working for a certain company, or I had a big mortgage and felt that I couldn't make many mistakes and get away with it. Then suddenly I was self-employed, I was getting lots of money in and I felt this real sense of liberation, so I dipped more than my toe in some murky waters. Now I understand as someone who's in the public eye, you just have to be extremely careful. I remember what the writer and critic W. Gordon Smith said to me, "Jack, you don't really need to do everything. You can go so far and let it roll through your mind. You know, you don't actually need to be the person in the middle of the room."

But people might dream of your level of success and see it as a route to complete freedom - do you feel free now?

No, I'm much more disciplined. I feel heavy responsibility for my family. I've been very generous with them, but I feel even more responsible for their minds if you like, because they're so proud of me - I mean awesomely proud - that to spoil that would just give me more pain than I could express to you.